1. Field of the Invention
The present invention relates generally to electrophotographic image forming equipment. More particularly, the present invention relates to a method of controlling the temperature of a cylinder used in the printing process for fixing a toner image.
2. Background Information
In most electrophotographic printing applications, the need exists for precision temperature control for maintaining adequate fusing roll temperature for the fusing of toner to a medium which is typically paper.
In most situations, the hot roller (or "fusing roll") is heated to a particular temperature at which it allows fusing of a toner to a medium. This temperature must be precisely controlled since, if the roller is too hot, the medium can be burned, or if the temperature is too cool, the toner will not adhere to the medium resulting in the image or words being smeared on the paper. Further, the temperature at which the hot roller must be kept varies with both the media on which information is printed and the characteristics of the toner. Typically, temperature is determined by a contact thermometer or thermocouple of some type in direct contact with the hot roll.
Current methods for controlling the temperature of a heated cylinder or roll are through the use of a ferrite chip that is charged with a magnetic field. The magnetic flux is then measured through a sensor, resulting in the generation of a pulse used to determine the cylinder's temperature. The ferrite chip fails to accept magnetic charge value when the optimum temperature is achieved, thus signaling the electronics of the printer that the required temperature has been reached since a pulse was not generated.
Another method of measuring cylinder temperature is through the use of contact thermal sensors and thermal fuses. These contact sensors measure the temperature of the heated roller through a heat transfer process dictated by positive contact with the surface of the hot roller.
What is needed is a non-contact temperature controlling device that can determine the ambient air temperature of a printer fixing or fusing device, measure the reflectance of a heated roller, and measure the temperature of a thermal coating applied to the heated roller used in the fixing of toner on a printed media. What is also needed is a non-contact temperature controlling device that is adjustable based upon media and toner characteristics and that is amenable to use by a layman operator of the printing system without special equipment or other specialized knowledge.